Polyamines are organic compounds having at least two primary amine groups, for example R—NH2. These compounds have a role in the metabolism of mammalian cells, translation, transcription and chromatin remodeling as well as the construction of the eukaryotic initiation factor eIF-5A. The polyamines play diverse roles within cells and many of their exact functions are not well described. It is known that cells can biosynthesize polyamines and that, if cellular polyamine biosynthesis is blocked, exogenously supplied polyamines may be imported into the cell via the so called polyamine transporter system (PTS).
Polyamines are synthesized in cells through highly regulated pathways, and maintaining cellular polyamine homeostasis is achieved through a balance of synthesis, degradation and import. They exist as polycations at physiological pH and are known to bind to DNA and other nucleic acids. In structure, they are aliphatic amines and at physiologic pH exist as polycations, where the cationic charges are found at regularly spaced intervals (unlike, say, Mg++ or Ca++, which are isolated point charges). In summary, polyamines are essential growth factors that cells require for proper growth and development.
When synthesis of cellular polyamines is inhibited, the cell's growth is also inhibited. Addition of exogenous polyamines to the extracellular milieu reactivates the growth of these cells. Most eukaryotic cells have a polyamine transporter system on their cell membrane that facilitates the import of exogenous polyamines. The polyamine transporter system (PTS) is highly active in rapidly proliferating cells and is the target of some chemotherapeutics currently under development. The current belief in the field is that cancer cells are unable to synthesize sufficient polyamines to sustain their rapid growth rates. Since many cancer cell lines have active polyamine transporters, it is possible to selectively target these cells via their need for polyamine growth factors and their active polyamine transport systems.